1. Field of the Invention
The present invention relates to a combustion state detection apparatus for an internal combustion engine, which detects abnormal combustion that has occurred in a combustion chamber of the internal combustion engine.
2. Description of the Related Art
In recent years, problems regarding environmental preservation, fuel exhaustion, and the like have been raised. For example, in the automotive industry, what measures are to be taken against those problems has been a serious challenge.
As the measures against those problems, a variety of technologies for maximizing engine efficiencies of internal combustion engines have been developed. However, on the contrary, occurrence frequencies of abnormal combustion in combustion chambers have been increased, causing such new problems as damage on internal combustion engines, decrease in durability thereof, and decrease in commercial value thereof.
Thus, in order to solve the above-mentioned problems, it is desired to detect abnormal combustion that has occurred in the combustion chamber, and to suppress the abnormal combustion in the case where the abnormal combustion has been detected.
A conventional combustion state detection apparatus for an internal combustion engine estimates a combustion pressure based on a detected ion current, determines that abnormal combustion has occurred in a combustion chamber in a case where a timing when the maximum value of the combustion pressure is obtained is on a spark-advance side compared with a predetermined reference timing, and executes abnormal combustion suppression processing such as increasing of an amount of fuel and delaying of an ignition timing (for example, refer to JP 2006-46140 A).
However, a problem described below has been inherent in the prior art.
In the conventional combustion state detection apparatus for an internal combustion engine, the combustion pressure of the internal combustion engine is estimated based on the ion current. However, in many cases, in an actual internal combustion engine, the maximum value of the combustion pressure generated as a result of the abnormal combustion is distributed immediately before ignition and immediately after ignition.
Here, immediately after ignition, a spark discharge for firing an air-fuel mixture in the combustion chamber is in progress, and a negative voltage is applied to an ignition plug. Accordingly, the ion current cannot be detected, and the combustion pressure cannot be estimated.
Therefore, the ion current cannot be detected with high accuracy during a period including before and after the ignition, resulting in such a problem that the abnormal combustion that has occurred in the combustion chamber cannot be detected with high accuracy.